There are numerous classic coating methods utilizing polymer materials to finish products of arbitrary shape.
In the particular field of surfboards, the oldest traditional method is a manual method: the float element with the required shape defined by a core, finished by manual sanding, is coated with an envelope of glass fibers impregnated with polyester or “epoxy” resin, which forms an external reinforcing shell and imparts to the float its final shape. Sanding a layer of pure paraffin-based resin then imparts to the float its final appearance. This traditional craft-oriented method is entirely manual.
The drawbacks of such a technique are that the products used are harmful and impact on working conditions, it takes a very long time and necessitates operatives, having particular qualifications, and finally the exterior shell has very low impact resistance. Moreover, the decoration possibilities are limited.
Industrial methods have therefore been developed for constructing the external shell of a float, either by rotary molding and injection of foam inside the shell formed in this way or by stacking different layers in a mold and press forming using heat and/or a vacuum.
The drawbacks of these industrial techniques are firstly that they necessitate the use of molds and do not allow personalization of the shape of the float, the shape of the external shell depending exclusively on the shape of the mold. Moreover, all boards manufactured in a mold always have a joint plane that is situated at the center of the edge of the board: for practical reasons of extraction from the mold it is impossible to position the joint plane elsewhere. This is the case for example of a board such as that described in patent application US 2008/0146102.
Accordingly, the joint plane of a float is always situated on the contour of the board and in the middle of the edge that is precisely the area most exposed to impact and the joint in the coating at this location makes the boards fragile. Moreover, the edge of the board is an area that is important from the smooth skimming point of view. Positioning the joint here disturbs the skimming of the float over the water. Finally, the joint plane at the center of the edge of the board is not esthetic and is not well thought of by users. Some manufacturers feel obliged to conceal it.
Where the equipment is concerned, the most classic automatic thermoforming methods that use molds to reproduce identical plastic parts (automobile hoods, point of sale displays, domestic appliance parts, food packaging, etc.) can be implemented using commercially available thermoforming machines. At present diaphragm presses enable parts of any type to be shaped, coated with glue and applied, but with no possibility of undercutting.
For arbitrary shapes formed from cores with plane main faces, such as those described in U.S. Pat. No. 5,728,246, for example, particular means have been adopted for covering the edges, which may be either convex or concave: the main teaching is that it is essential to limit the overshoot of the sheet that is to cover the edge, notably to avoid creases: there is never provision for undercutting on the face opposite the face covered mainly by a sheet of polymer material.
Patent application DE 10254957 describes, for the production of furniture or indoor equipment elements, a method of producing panels formed in a vacuum press where a first face is entirely covered with a facing sheet after which the second face and the edge are covered by a second sheet, with the result that finishing is facilitated but the finishing joint line is exactly in the corner formed by the first face and the edge, which the invention seeks to avoid.